Gear pump



M. TUROLLA GEAR PUMP April 9, 1968 3 Sheet Sheet' 1 Filed June 27, 1966INVENTOR MARco TUROLLA BY p Q I v ATTORNEYS M. TUROLLA April 9, 1968GEAR PUMP 3 Sheets-Sheet Filed June 27, 1966 MARCO TuRoLLA BY /0 x v 9 4Z I ATTORNEYS April 1968 M. TUROLLA 3,376,824

I GEAR PUMP Filed June 27, 1966 3 Sheets-Sheet 5 105 INVENTOR Fig.10

MARco TUROLLA ATTORNEYS United States Patent 12 Claims. (Cl. 103-126)This invention relates to a gear pump in which a sealing plateresiliently bendable in axial direction has its periphery fastened inthe pump case, is situated at one side of the gears at least, and may bepressed against the corresponding lateral surface of the gears byhydraulic pressure which is generated in a pressure chamber situated atthe outer side of the sealing plate and connected to the delivery sideof the pump.

In known gear pumps of this kind, the sealing plate is of uniformthickness throughout and its bendability is thus limited, particularlysince the overall thickness of the sealing plate must be relativelygreat for structural reasons. Since the sealing plate moreover has itsentire periphery clamped in the pump case, it is deformed inwards inpot-like or cap-like manner, i.e. to dome-shape, by the deliverypressure of the pump acting on its outer side, so that a limited medianportion of it can bear in sealing manner on a correspondingly limitedportion of the lateral gear surfaces. At the side of the gears facingthe sealing plate, leaks thus develop between the suction and pressuresides of the pump, causing substantial pressure losses, whichconsiderably reduce the elliciency of the pump.

The main object of the present invention is to provide a gear pump inwhich these disadvantages are avoided and to influence the bendabilityof the sealing plate while retaining its required strength, so that thedelivery pressure of the pump acting on the outer side of the sealingplate presses the plate as flat as possible and with a substantiallygreater proportion of its inner surface against the correspondinglateral surfaces of the gears, thereby forming a better seal between thesuction and delivery sides of the pump than in the known pumps.

According to the present invention, a gear pump comprises a pump case, apair of gears rotatably mounted in cavities in the case, inlet andoutlet opening in the case communicating with the gear cavities, asealing plate mounted in the case at one side of the gears andresiliently bendable axially of the case and clamped at its periphery inthe case, a pressure chamber in the case on the side of the plate remotefrom the plate and in communication with the ressure side of the pump,the hydraulic pressure generated in the pressure chamber urging theplate into engagement with lateral surfaces of the gears, and aweakening groove in the plate which at least of the pressure side of thepump has an outline approximating to the circumferential profile of thegears.

This weakening groove preferably also extends on the suction side of thepump and has an annularly closed conformation. This outer weakeninggroove of the sealing plate is appropriately also acted upon by thedelivery pressure of the pump. To this end, the weakening groove may bein communication with the pressure chamber arranged on the outer side ofthe sealing plate and in communication with the pressure side ofthepump. In an advantageous and particularly simple pump the externalpressure chamber is in the form of a median fiat or shallow depressionin the outer side of the sealing plate, and the much deeper weakeninggroove is arranged in the area of this depression, preferably along itsexternal boundary thereof. The outer weakening groove and the shallowexternal depression of the sealing plate may be of approximately ovalform, which may be slightly constricted or waisted in the middle, i.e.in the meshing area of the gears.

The shape of the outer weakening groove divides the sealing plate intoan outer marginal portion secured in the pump case and a median portioncorresponding to the gears and cooperating with their correspondinglateral surfaces, this median portion having the same or a lesserthickness than the marginal portion secured in the pump case and beingjoined to the latter by a much thinner and thus much more yielding webin the area of the weakening groove. As a result, the sealing plate,when acted upon by delivery pressure of the pump on its outer side,behaves like a diaphragm reinforced in the middle, i.e. only the thinnerjoining web between the median and marginal parts of the sealing platebeing deformed resiliently, whilst the median part of this plate boundedby the weakening groove is but slightly domed inwards and is displacedand pressed against the gears approximately parallel to itself withretention of a substantially plane form. The sealing plate is thuspressed with area contact against a substantially greater part of thelateral surfaces of the gears and effects lateral sealing of the gearcompartment.

According to a further feature of the invention, the outer weakeninggroove of the sealing plate has a varying depth, increasing at eitherside from the suction side of the pump in the peripheral directiontowards its pressure side. The joining web left in the area of thisweakening groove between the median and external immobilised marginalpart of the sealing plate is thus thinner, more pliable and moreresilient at the pressure side than at the suction side of the pump. Themedian part of the sealing plate bounded by the weakening groove is thuspressed against the gears with a force which increases progressivelyfrom the suction side to the pressure side of the pump according to thepliability and resiliency of the said joining web. The distribution ofthe pressure of contact of the sealing plate against the gears is thusadapted in the simplest manner to the internal pressure of the pump,which is not uniformly distributed across the pump cross-section, asknown, but rises progressively from the suction side of the pump towardsits pressure side.

The advantageous action of the sealing plate of the invention may befurther improved by forming the weakening groove as a slit passingthrough the thrust plate at the pressure side of the pump, the slitbeing of limited length and preferably extending symmetrically to themedian transverse axis of the pump cross-section lying between thegears. In this embodiment, the median part of the sealing platepartially bounded by the slit is separated even more from the marginalpart of this plate secured in the pump case, so that it bends even lesson being thrust against the gears and retains its plane form with evengreater reliability. At the same time, the contact pressure of thesealing plate against the gears is substantially increased at thepressure side of the pump, and can in practice assume an optimumapproximately equal to the delivery pressure of the pump. The contactpressure of the sealing plate is thus adapted more adequately to theirregularly distributed internal pressure of the pump.

Together with or instead of the slit in the sealing plate, the outerweakening groove may moreover be omitted along a limited peripheralstretch on the suction side of the pump. This reduces or eliminates thecontact pressure of the sealing plate at the suction side of the pumpand the thrust exerted by the sealing plate on the gears is equallybetter adapted to the asymmetrical distribution of the internal pressureof the pump.

In order that the invention may be more fully understood someembodiments in accordance therewith will now be described by way ofexample with reference to the accompanying drawings in which:

FIG. 1 shows a longitudinal cross-section through a gear pump;

FIG. 2 is a cross-section along the line IIII of FIG. 1;

FIG. 3 is a cross-section along the line III-III of FIG. 2;

FIG. 4 shows a cross-section of the dismantled sealing plate along theline IVIV of FIG. 2;

FIG. 5 shows a longitudinal cross-section of another construction ofgear pump;

FIG. 6 is a cross-section along the line VIVI of FIG. 5;

FIG. 7 is a cross-section along the line VII-VII of FIG. 6;

FIG. 8 is a cross-section of the dismantled sealing plate of the pump ofFIGS. 5 to 7;

FIG. 9 shows diagrammatically the mode of operation of the conventionalsealing plate in a known pump; and

FIG. 10 shows diagrammatically the mode of operation of the sealingplate in a pump of the invention.

In both the construction shown in the drawings, the gear pump comprisesa middle case 3 having bores for two meshing gears 4 and 5, between twolateral case covers 1, 2. A steel sealing plate 6 is disposed at oneside of the gears 4, 5 between the case 3 and the case cover 2. Thecover 2 has a radially projecting flange 102 which may serve to fastenthe pump on a bearing element (not shown). The two case covers 1, 2, themiddle case 3 and the sealing plate 6 are interconnected by axiallyparallel through-bolts 7, the plate 6 thus being firmly clamped with itsmarginal part between the middle case 3 and the case cover 2.

The gears 4, 5 have lateral spindles 104, 204 and 105, 205,respectively, rotatably mounted in bores of the covers 1, 2. The bearingbores for the spindles 104, 105, 205 are formed as blind holes, whereasthe extended spindle 204 of the gear 4 passes through and out of thecover 2 and forms the driving shaft of the pump. The gear spindles 204,205, facing the sealing plate 6 pass through appropriate bores 8therein, the inner diameter of these bores 8 being greater than theouter diameter of the gear spindles 204, 205 so as not to impede thedeflection or deformation of the median, non-clamped part of the sealingplate in the axial direction of the pump. The suction passage 9 and thepressure outlet passage 10 of the pump are provided in the case cover 1and open into a suction space 109 and pressure space 110 respectively ofthe middle case 3, as seen in FIGS. 3 and 7.

In the construction of FIGS. 1 to 4, the cover 1 on the side of themiddle case 3 remote from the sealing plate 6 bears directly on themiddle case 3. The seal between the middle case 3 and the adjacent cover1 on the one hand, and between the middle case 3 and the marginal partof the sealing plate 6 on the other hand, is provided by annular endjoints 11, 12 respectively disposed as far as possible beyond thecircumferential outline of the pair of gears 4, 5. An analogous endjoint 13 is disposed between the marginal part of the sealing plate 6and the other case cover 2. Between the sealing plate 6 and the adjacentcover 2 an annular end joint 14 is arranged around the passage bore 8 ofeach gear spindle 204, 205.

In the external side of the sealing plate 6 facing away from the gears4, 5, there is a relatively deep annularly closed weakening groove 15within the area bounded by the outer joint 13, this groove having aprofile approximating to the outer profile of the pair of gears 4, 5,i.e. approximately oval and with a constriction in the middle, as seenin FIG. 2. This weakening groove 15 has a varying depth increasing ateither side from the suction side of the pump towards its pressure side,so that its smallest depth is reached at say the point A in FIG. 2, andits 4 greatest depth at say the point B in FIG. 2, as also seen in FIGS.3 and 4.

In the outer side of the sealing plate 6 there is moreover a flatdepression 16 which is bounded externally by the weakening groove andinternally by two annular end joints 14, and thus is of approximatelyfigure-8 shape. At its outer periphery, this depression 16 merges intothe weakening groove 15 and in combination with the cover 2 forms apressure chamber, in communication with the weakening groove 15 on theone hand and with the pressure side of the pump on the other. Connectionto the pressure side of the pump is established through a cavity 17 inthe inner side of the sealing plate in the area of the pump pressurespace and in communication with the space 110, which cavity is connectedto the pressure chamber 16 through a bore 18. Symmetrically of thecavity 17, an analogous cavity 19 is provided in the inner side of thesealing plate, which is in communication with the suction side or thesuction chamber 109 of the pump, but not with the pressure chamber.

In operation, the delivery pressure of the pump prevailing in thepressure chamber 16 and in the weakening groove 15 acts on the outerside of the sealing plate 6. The sealing plate is thus pressed inwardsresiliently and its plate inner side is pressed in axial directionagainst the corresponding plane lateral surface of the gears 4, 5. Onlythe thinner, more pliable and more resilient web 106 is therebypreferentially deformed, which web is formed in the area of theweakening groove 15 and connects the rigid thicker median part 206 ofthe sealing plate 6 bounded by the weakening groove 15 with the outermarginal part 306 of the sealing plate secured between the case 3 andthe cover 2. The median part 206 of the sealing plate 6 pressed againstthe gears thus es- F sentially retains its plane form, i.e. it is notexcessively bent or deformed inwards, so that it bears against the gearsin area contact and with sufiicient surface area to provide the requiredlateral sealing of the pump spaces. At the same time, the sealing plate6 is pressed against the gears 4, 5 with a force rising progressivelyfrom the suction side to the pressure side of the pump, since the depthof the weakening groove 15 and thus the pliability or deformability ofthe corresponding joining web 106 inreases at either side from thesuction side (point A) towards the pressure side (point B). Thisirregular distribution of contact pressure corresponds to thedistribution of the opposed internal pressure of the pump, so that thelatter is balanced evenly, as will be described.

In FIG. 1, the driving spindle 204 of the gear pump is driven through anextension shaft 20 which is rotatably secured in an additional casing 21releasably fastened to the pump case, and is coupled in formlocked andforcelocked manner with the driving shaft 204 of the pump. The bearingcasing 21 of this extension shaft 20 is inserted with a centering ring22 on an outer boss 23 of the pump cover 2 and secured by screwbolts 24on the outer flange 102 of the cover 2. The extremity of the extensionshaft 20 mounted in a roller bearing or ball bearing 25 in the case 21,i.e. facing towards the pump spindle 204, has a blind co-axial bore 26with a longitudinally grooved inner side. In this bore engages theconical extremity of the pump spindle 204 projecting from the pump cover2, on which is placed a coupling sleeve or the like 27 with acorrespondingly conical bore. This coupling sleeve 27 is secured inrotatory manner on the pump spindle 204 by a key 28 and a nut 30 screwedon an externally threaded pin 29 on the pump spindle 204. The couplingsleeve 27 has a longitudinally grooved or splined outer surface and isin engagement with the correspondingly splined inner side of the blindbore 26 in the extension shaft 20, 120. ,This connects the two spindles20, 204 in a rotatory manner. This arrangement has the advantage thatthe bending stresses applied by the driving means on the projectingunconfined extremity of the extension shaft 20 are absorbed by the ballor roller hearing 25, and by the additional bearing case 21 and are nottransmitted .to the pump spindle 204. At the same time, the clearancebetween the splined coupling elements 120, 27 allows small deviations inalignment between the axes of the two spindles.

Referring to FIGS. 5 to 8, these show a gear pump in which aninter-mediate plate 31 is disposed between the cover 1 and the middlecase 3 at the opposite side of the gears from the sealing plate 6, whichplate has bores 209, 210 in the area of the suction and pressurepassages 9, for connection of these passages with the suction andpressure spaces 109, 209 of the case 3. The seal between thisintermediate plate 31 and the cover 1 on the one hand, and the middlecase 3 on the other, is established by annular end joints 32, 33. Aroundthe traverse bores 8 of the gear spindles 204, 205, annular end joints14 are disposed between the sealing plate 6 and the cover 2. Thepressure chamber on the outer side of the sealing plate 6 is againformed by a flat or shallow depression 16 in the outer side of thesealing plate 6, corresponding to the peripheral profile of the pair ofgears 4, 5 and inwardly bounded by the joints 14, so that it is ofapproximately figure-8 form. The outer side of the sealing plate 6 alsohas a weakening groove which extends along the circumferential boundaryof the depression 16 and is in communication therewith. Compared to thepump of FIGS. 1 to 4, the weakening groove 15 does not however extendalong the entire periphery of the pressure chamber 10, i.e. is not aclosed circuit annularly, but is interrupted on the suction side of thepump and is of approximately figure-3 shape terminating at C and Dapproximately at the levels of the axes of the gears. At the pressureside of the pump, this weakening groove is made in the form of a slitpassing through the sealing plate 6 along a limited longitudinal sectionEF. In its middle portion G, this slit 35 is in communication with thepressure space 110 of the pump and accordingly establishes communicationbetween the pressure chamber 16 and the pressure side of the pump. Thesections C-E and D-F of the weakening groove 15 have a depth increasingfrom the suction side of the pump towards its pressure side, seen inFIG. 8.

The mode of operation of the gear pump of FIGS. 5 to 8 essentiallycorresponds to that of FIGS. 1 to 4 and will be described in greaterdetail with reference to FIGS. 9 and 10. In FIG. 9, a detail of a knowngear pump is shown, in which the sealing plate 60 lacks an outerweakening groove and is of the same thickness throughout. In this knownconstruction, the sealing plate 60 acts like a uniformly bendablediaphragm clamped on all sides, and is thus bent inwards to dome-shapeby the delivery pressure of the pump acting on its outer side, asindicated in dash-dotted lines in FIG. 9. As a result, only a relativelysmall part of its inwardly convex middle portion comes into contact withthe corresponding lateral surface of the gears. This contact area isnormally too small to provide satisfactory lateral sealing of the gears.The sealing plate 60 is moreover pressed against the gears with the sameforce at the suction side and pressure side of the pump. This uniformdistribution of contact pressure does not however correspond to thedistribution of internal pump pressure, which as known risesprogressively from the suction side to the pressure side of the pump.The force directed inwards, i.e. against the gears, resulting from theuniformly distributed pressure on the outer side of the sealing plate 60and from the irregularly distributed counterpressure on its inner side,is displaced towards the suction side of the pump out of the medianplane of the pump passing through the axes of the gears. This offsetthrust loading results in correspondingly irregular friction between thelateral surfaces in contact with the sealing plate 60 and gears, so thatthe inner surface of the sealing plate 60 wears more quicklyat thesuction side of the pump. This offset thrust loading moreover causesundesirable transverse loading of the gear spindles and correspondingunilateral wear of their bearings.

FIG. 10 shows the mode of operation of the sealing plate 6 with aweakening groove 15 and a corresponding slit 35, as in FIGS. 5 to 8. Inthis construction the middle portion 206 of the sealing plate 6 islargely separated from the outer marginal part 306 of the sealing plate6 secured in the pump case, being partially bounded by the weakeninggroove 15 and partially by the slit, being wholly separated in the areaof the slit 35 from the marginal part 306, and being connected to themarginal part 306 in the area of the sections CE and D-F of theweakening groove 15 through the thinner and thus more pliable andresilient joining web 106, as seen in FIG. 8. As a result, the middleportion 206 of the sealing plate 6 is only slightly domed inwards by thedelivery pressure of the pump acting on the outer side, and is pressedalmost parallel to itself and with retention of an approximately planeform, against the lateral surface of the gears, as shown in dash-dottedlines in FIG. 10. There is no bending at all of the sealing plate 6 inthe area pf the slit 35, whereas in the area of the sections C-D and D-Fof the weakening groove 15, only the more resilient joining web 106 isdeformed resiliently and preferentially. This ensures a more completecontact of the sealing plate 6 with a substantially greater part of thecorresponding lateral surface of the gears and thus better lateralsealing compared with the known constructions.

At the same time, the middle part 206 of the sealing plate 6 is pressedagainst the gears with a greater force at the pressure side of the pumpthan at its suction side, since the pressure-side section of the medianpart 206 of the sealing plate is wholly separated from the immobilemarginal part 306 of the sealing plate 6 by the slit 35, whereas thesuction side section of the said middle part 206 merges into themarginal part 306 without any weakening. The intermediate sections C-Dand D-F of the weakening groove extending around the gears, by virtue oftheir progressively increasing depth, cause the contact pressure of thesealing plate 6 against the gears to rise continuously from the suctionside towards the pressureside of the pump. This asymmetricaldistribution of the contact pressure approximately corresponds to theintenal pump pressure distribution, so that the resulting inwardlydirected force acts approximately in the median plane of the pumppassing through the axes of both gears. This produces an even frictionbetween the sealing plate 6 and the gears, and prevents undesirabletransverse loadings of the gear spindles.

The gear pump may be provided with two sealing plates with weakeninggrooves 15 and slits 35 at either side of the gears.

What is claimed is:

1. A gear pump com-prising a pump case, a pair of gears rotatablymounted in cavities in said case, inlet and outlet openings in said casecommunicating with said gear cavity, a sealing plate mounted at one-sideof said gears resiliently bendable axially of said case and clamped atits periphery in said case, a pressure chamber in said case on the outerside of said plate and in communication with the pressure side of saidpump, the hydraulic pressure generated in said chamber urging said plateagainst the lateral surfaces of said gears, and a weakening groove insaid plate which at least at said pressure side of said pump has anoutline approximating to the circumferential profile of said gears.

2. A gear pump according to claim 1 wherein said groove extends over thesuction side of said pump and has an annular closed contour.

3. A gear pump according to claim 1 wherein said groove has an ovalcontour slightly waisted in the meshing area of said gears.

4. A gear pump according to claim 1 wherein said groove has a figure-3shape, interrupted at the suction side of said pump.

5. A gear pump according to claim 1 wherein said groove is incommunication with said pressure chamber.

6. A gear pump according to claim 1 wherein said pressure chambercomprises a median shallow depression in said outer side of said plateand said weakening groove is substantially deeper than said depressionand is disposed in the region of said depression.

7. A gear pump according to claim 1 wherein said pressure chambercomprises a median shallow depression in said outer side of said plateand said weakening groove is along the external boundary of saiddepression.

8. A gear pump according to claim 1 wherein the depth of said grooveincreases at either side in the peripheral direction from the suctionside towards the pressure side of said pump.

9. A gear pump comprising a pump case, a pair of gears rotatably mountedin cavities in said case, inlet and outlet openings in said casecommunicating with said gear cavity, a sealing plate mounted at one sideof said gears resiliently bendable axially of said case and clamped atits periphery in said case, a pressure chamber in said case on the outerside of said plate and in communication with the pressure side of saidpump, the hydraulic pressure generated in said chamber urging said plateagainst the lateral surfaces of said gears, and a weakening groove insaid plate which at least at said pressure side of said pump has anoutline approximating to the circumferential profile of said gears,

said groove being in the form of a slit of limited length traversingsaid plate on the pressure side of said pump.

10. A gear pump according to claim 9 wherein said slit extendssymmetrically to the median transverse axis of said pump cross-sectionbetween said gears.

11. A gear pump according to claim 9 wherein said pressure chamber isconnected to the pressure side of said pump through said slit.

12. A gear pump according to claim 9 wherein bores are formed in saidplate and said gears are mounted on spindles journalled in said case andpassing through said bores, said bores having a substantially greaterdiameter than said spindles.

References Cited UNITED STATES PATENTS 164,147 6/1875 Conver 103-1262,544,988 3/1951 Gardiner et al 103135 2,702,509 2/1955 Garnier 1031262,809,592 10/1957 Miller et a1 103-426 3,019,737 2/1962 Plrasse 103-1263,204,566 9/1965 Feroy 103-126 3,280,754 10/1966 Marietta 103-126 DONLEYJ. STOCKING, Primary Examiner.

W. I. GOODLIN, Assistant Examiner.

1. A GEAR PUMP COMPRISING A PUMP CASE, A PAIR OF GEARS ROTATABLY MOUNTEDIN CAVITIES IN SAID CASE, INLET AND OUTLET OPENINGS IN SAID CASECOMMUNICATING WITH SAID GEAR CAVITY, A SEALING PLATE MOUNTED AT ONE SIDEOF SAID GEARS RESILIENTLY BENDABLE AXIALLY OF SAID CASE AND CLAMPED ATITS PERIPHERY IN SAID CASE, A PRESSURE CHAMBER IN SAID CASE ON THE OUTERSIDE OF SAID PLATE AND IN COMMUNICATION WITH THE PRESSURE SIDE OF SAIDPUMP, THE HYDRAULIC PRESSURE GENERATED IN SAID CHAMBER URGING SAID PLATEAGAINST THE LATERAL SURFACES OF SAID GEARS, AND A WEAKENING GROOVE INSAID PLATE WHICH AT LEAST AT SAID PRESSURE SIDE OF SAID PUMP HAS ANOUTLINE APPROXIMATING TO THE CIRCUMFERENTIAL PROFILE OF SAID GEARS.